CN213275196U

CN213275196U - Direct shear test device for freeze-thaw interface of soil body

Info

Publication number: CN213275196U
Application number: CN202021926347.6U
Authority: CN
Inventors: 何鹏飞; 穆彦虎; 黄永庭; 栗晓林; 马巍
Original assignee: Northwest Institute of Eco Environment and Resources of CAS
Current assignee: Northwest Institute of Eco Environment and Resources of CAS
Priority date: 2020-09-07
Filing date: 2020-09-07
Publication date: 2021-05-25
Anticipated expiration: 2030-09-07

Abstract

The application relates to a soil body freeze thawing interface direct shear test device, including last shear box (2), lower shear box (3), refrigeration mechanism, temperature measurement part and temperature controller (17), its characterized in that: the refrigeration mechanism is arranged at the bottom of the lower shearing box (3), the upper shearing box (2) and the lower shearing box (3) are respectively provided with a temperature measuring component at the side wall close to the shearing surface, and a micro gap is formed between the upper shearing box and the lower shearing box after the assembly is finished; the temperature controller (17) is connected with the refrigerating mechanism and the two temperature measuring components. This application can realize that the soil sample is along the one-way temperature control of vertical direction, and then realizes at the freeze thawing interface of specific position, and cooperation direct shear appearance power device can develop the experiment to the shearing characteristic of soil body freeze thawing interface to temperature controller (17) provide the assurance for the experimental precision according to temperature feedback automatic control function in the shearing box, shearing box heat-insulating material's use.

Description

Direct shear test device for freeze-thaw interface of soil body

Technical Field

The application relates to the technical field of geotechnical tests, in particular to a direct shear test device for a freeze-thaw interface of a soil body.

Background

China is the third world with frozen soil distribution, the perennial frozen soil area occupies about 21.5% of the territory of China, and the seasonal frozen soil area occupies about 53.5% of the territory of China. Therefore, frozen soil is a valuable land resource. Since the beginning of the new century, research on physical and mechanical properties of frozen soil is widely concerned due to the close combination of scientific research and production and the major national projects such as Qinghai-Tibet railway, Chuanghai-Tibet railway, Qinghai-Tibet ultra-high voltage transmission line, Qinghai-Tibet expressway and the like.

However, due to the influence of human activities (engineering construction, excavation and soil taking, and the like) and natural environment changes (climate warming, river erosion, permafrost melting, and the like) on the original soil physical and mechanical fields, engineering for building in frozen soil areas faces many problems, one of which is slope collapse in permafrost areas and seasonal frozen soil areas. The reason for causing the soil slope to collapse is that the water in the active layer and the seasonal frozen soil layer seeps in the spring thawing process, a water-retaining lubricating interface is formed at the interface position of the frozen soil body, and the soil body shear strength at the interface is obviously reduced. The self weight of the upper melt soil is increased along with the increase of the melting depth, and finally the self weight of the upper soil body cannot be supported due to the strength of the freezing and thawing interface to cause slumping. Therefore, the research on the shear strength characteristics of the soil body freezing and thawing interface is the key point for predicting and solving the problem of freezing and thawing slumping.

In the prior art, the existing frozen soil direct shear apparatus can realize the integral freezing or melting effect of a soil body, such as application No. 201110221970.0 and a full-automatic digital large-scale frozen soil direct shear apparatus, but because the schemes are all through integral cooling or side wall cooling, temperature control in the direction perpendicular to a shear plane cannot be realized, coincidence of a freezing and thawing interface and the shear plane cannot be really realized, and further the stress state of the soil body freezing and thawing interface in an actual environment cannot be really simulated, so that a large difference exists between a test result (stress-strain relation of the soil body freezing and thawing interface, an interface shear strength parameter and the like) and an actual situation, and a research value of the test result is lost. In addition, the cooling bath or liquid nitrogen is used for cooling, so that the price is high, the noise is high, and the occupied space is large.

Disclosure of Invention

The technical problem that this application will be solved provides a soil body freeze thawing interface direct shear test device that experimental result more is close actual conditions.

In order to solve the problem, the application provides a soil body freeze thawing interface direct shear test device, including last shear box, lower shear box, refrigeration mechanism, temperature measurement part and temperature controller, its characterized in that: the refrigeration mechanism is arranged at the bottom of the lower shearing box, the temperature measuring components are respectively arranged on the side walls of the upper shearing box and the lower shearing box close to the shearing surface, and a micro gap is formed between the upper shearing box and the lower shearing box after the assembly is finished; the temperature controller is connected with the refrigerating mechanism and the two temperature measuring components and used for controlling the working condition of the refrigerating mechanism according to the real-time temperature values of the two temperature measuring components after the preparation work is finished so as to enable the two temperature measuring components to reach respective preset target temperature values, and further forming a freeze-thaw interface.

Preferably, the refrigerating mechanism comprises a semiconductor refrigerator and a cold storage plate arranged on the semiconductor refrigerator, and the upper surface of the cold storage plate is in direct contact with the soil sample in the lower shear box during operation.

Preferably, the refrigeration mechanism further comprises a radiator arranged at the bottom of the semiconductor refrigerator.

Preferably, the refrigerating mechanism further comprises heat-conducting silica gel arranged between the semiconductor refrigerator and the cold storage plate.

Preferably, the upper shear box and the lower shear box are made of materials with small heat conductivity coefficients.

Preferably, the material with low thermal conductivity is organic glass.

Compared with the prior art, the method has the following advantages:

1. this application is through refrigeration mechanism from 3 bottoms of lower shear box upwards cooling along the direction of perpendicular to shear plane, can realize that the soil sample along the one-way temperature control of vertical direction realize promptly with shear plane vertically temperature gradient distribution, and then realize the freeze thawing interface at the specific position (cut box juncture from top to bottom), the cooperation staight scissors appearance power unit can develop the experiment to the shear characteristic of soil body freeze thawing interface. And the temperature controller has the function of automatic control according to the temperature feedback in the shearing box, so that the control of the position of the soil body freezing and thawing interface in the direction vertical to the shearing surface can be accurately realized, and the precision guarantee is provided for the soil body freezing and thawing interface direct shear test.

2. Compared with the cooling bath or liquid nitrogen cooling in the prior art, the semiconductor cooling method used by the refrigerating mechanism has the advantages of low cost, small occupied space, low noise and high efficiency.

3. This application further sets up adiabatic boundary all around through the organic glass who has adiabatic effect cuts the box through the use organic glass and sets up the adiabatic boundary in soil sample upper portion through the organic glass upper cover, has further guaranteed test accuracy.

4. In practical application, the shear box of the present application can be made to be identical in size and structure to a standard shear box, thereby being capable of matching with a 1-gang or 4-gang direct shear apparatus proposed in the geotechnical test code (SL 237-1999) to achieve the effects of cost reduction and rapid use.

Drawings

The following describes embodiments of the present application in further detail with reference to the accompanying drawings.

Fig. 1 is a schematic overall structure diagram of a soil body freeze-thaw interface direct shear test device provided in an embodiment of the present application.

Fig. 2 is a right side view of a soil body freeze-thaw interface direct shear test device provided in an embodiment of the present application.

Fig. 3 is a top view of an upper shear box provided in an embodiment of the present application.

Fig. 4 is a top view of a lower shear box provided in an embodiment of the present application.

FIG. 5 shows the results of finite element modeling of shear plane temperatures provided in embodiments of the present application.

In the figure: 1-pressure plate, 2-upper shear box, 3-lower shear box, 4-first horizontal load rod, 5-second horizontal load rod, 6-shear box base, 7-sliding ball, 8-soil sample in upper shear box, 9-soil sample in lower shear box, 10-cold storage plate, 11-semiconductor refrigerator, 12-radiator, 13-fan, 14-safety net, 15-first temperature sensor, 16-second temperature sensor, 17-temperature controller, 18-power supply.

Detailed Description

Referring to fig. 1 to 4, the embodiment of the present application provides a direct shear test device for a soil freezing-thawing interface, which mainly comprises an upper shear box 2, a lower shear box 3, a refrigeration mechanism, a temperature measurement component and a temperature controller 17; wherein, the upper shearing box 2 and the lower shearing box 3 are shearing parts, and the refrigerating mechanism, the temperature measuring part and the temperature controller 17 are temperature control parts. The refrigeration mechanism is arranged at the bottom of the lower shearing box 3, the side walls of the upper shearing box 2 and the lower shearing box 3 close to the shearing surface are respectively provided with a temperature measuring component (used for detecting the temperature value of the soil sample at the interface), and a micro gap is formed in the middle of the upper shearing box 2 and the lower shearing box 3 after the assembly is completed and is used for enabling the freeze-thaw interface to be completely coincided with the shearing surface.

The temperature controller 17 is connected with the refrigeration mechanism and the two temperature measurement components, and is used for controlling the working condition (start-stop state) of the refrigeration mechanism according to the real-time temperature values of the two temperature measurement components after the preparation work is finished, so that the two temperature measurement components reach respective preset target temperature values, and further the formation of a freeze-thaw interface is realized.

The temperature measuring means includes a first temperature sensor 15 and a second temperature sensor 16. A temperature sensor hole is formed in the side wall, close to the shearing surface, of the upper shearing box 2, and is used for mounting the first temperature sensor 15, meanwhile, a temperature sensor hole is formed in the side wall, close to the shearing surface, of the lower shearing box 3, and is used for mounting the second temperature sensor 16, and then a ceramic rod temperature probe is mounted in the temperature sensor hole.

The design of 3 lateral walls lower parts of lower shear box has shear box base 6, and slip ball 7 is installed to the base lower part, and slip ball 7 is established on the support for lower shear box 3 (together with the refrigeration mechanism of its bottom) can slide along the shearing direction on the staight scissors appearance platform, and keeps lower frictional resistance, thereby improves the experimental accuracy of interface shear.

In practice, the shear part comprises, in addition to the upper shear box 2 and the lower shear box 3, a first horizontal load bar 4 and a vertical load member respectively provided at the side wall and the top of the upper shear box 2, and a second horizontal load bar 5 opposite to the first horizontal load bar 4 at the side wall of the lower shear box 3. The first horizontal load bar 4 and the second horizontal load bar 5 are used for being in flexible connection with an external power device so as to measure shearing force change and shearing deformation in the shearing process.

In this application, vertical loading spare is the pressure plate 1 of directly establishing 8 upper surfaces of soil sample in the box of last shearing. The pressure plate 1, the upper shear box 2 and the lower shear box 3 are all made of materials with small heat conductivity coefficient, such as organic glass (PMMA). The thermal conductivity coefficient of the organic glass is about 0.18W/mK, which is far lower than that of a metal material, and the organic glass has good heat preservation effect.

In this application, refrigeration mechanism establishes in 3 bottoms on the box of cuting down for from 3 bottoms on the box of cuting down and begin along the direction of perpendicular to shear plane cooling down upwards. The refrigerating mechanism specifically comprises a semiconductor refrigerator 11 and a cold storage plate 10 arranged on the semiconductor refrigerator 11, and the upper surface of the cold storage plate 10 is in direct contact with the soil sample in the lower shear box 3 during operation.

The semiconductor temperature control principle is that by means of the Peltier effect of semiconductor material, when DC passes through a couple formed by two different semiconductor materials connected in series, heat can be absorbed and released at two ends of the couple respectively, so that the purpose of refrigeration can be achieved. The refrigerating technology which generates negative thermal resistance is characterized by no moving parts and higher reliability.

In practical application, the cold storage plate 10 may be made of copper material, and a fine hole is opened in the middle to reduce the deformation of the cold storage plate during the temperature variation process; the copper material has high thermal conductivity coefficient (about 381W/mK), fast temperature transmission and uniform temperature distribution at the bottom of the soil sample 9 in the lower shear box. The refrigerating power of the semiconductor refrigerator 11 is 35W, the stable current is 3.9A, and the voltage is 12V.

The refrigerating mechanism also comprises a radiator 12 arranged at the bottom of the semiconductor refrigerator 11 and used for discharging heat generated at the radiating end of the semiconductor refrigerator 11; in practical applications, the heat sink 12 may be composed of a fan 13 and a safety net 14, and a space for accommodating the fan 13 is erected between the safety net 14 and the heat dissipating end of the semiconductor cooler 11. The refrigerating mechanism further comprises heat-conducting silica gel which is arranged between the semiconductor refrigerator 11 and the cold storage plate 10 and is filled with a gap, and the heat-conducting silica gel is used for enhancing the temperature conduction efficiency.

Based on the above content, practical application and use (test) method of the soil body freezing-thawing interface direct shear test device are described by way of example.

The pressure plate 1, the upper shearing box 2 and the lower shearing box 3 are all made of organic glass. The side wall thickness of the upper shearing box 2 and the lower shearing box 3 is 20 mm, and the diameter of the middle soil sample bin is 61.8 mm. The upper pressurizing plate 1 is conical, the edge thickness is 10 mm, the center thickness is 20 mm, the lower diameter is 61.8 mm, and the upper pressurizing plate is matched with the soil sample bins in the shearing box.

The temperature controller 17 has the temperature measuring range of minus 50 ℃ to 110 ℃, the temperature measuring precision of plus or minus 0.1 ℃, the refreshing frequency of 0.5s, the temperature control range of minus 40 ℃ to 100 ℃ and the temperature control precision of 0.1 ℃. The temperature controller 17 is powered by a 12V dc power supply 18.

The test method comprises the following steps:

1. and (3) manufacturing a cylindrical soil sample by using a sample press, wherein the soil sample is made of silty clay, the height of the soil sample is 40 mm, and the diameter of the soil sample is 61.8 mm. The water content and the dry density of the soil sample are specifically determined according to the test requirements.

2. Wrapping the prepared soil sample with a plastic film to prevent water from losing, placing the wrapped soil sample in a constant temperature box, setting the temperature to be 5 ℃ and standing for 12 hours to enable the temperature field in the soil body to be uniform.

3. The soil sample is loaded into the upper shear box 2 and the lower shear box 3 (the soil sample 8 in the upper shear box and the soil sample 9 in the lower shear box are integrated before shearing), and a vertical load is applied through the pressurizing plate 1.

4. And starting the temperature controller 17, firstly setting the target temperature values of the two temperature sensors to be 2 ℃, starting the semiconductor refrigerator 11 to work, and slowly cooling upwards from the bottom of the lower shearing box 3 along the direction vertical to the shearing surface.

5. After the temperature at the interface measured by the temperature sensor reaches 2 ℃ and is stably maintained for more than 30min, the target temperature value of the second temperature sensor 16 is set to-0.2 ℃, the target temperature value of the first temperature sensor 15 is set to 0.2 ℃, and the semiconductor refrigerator 11 starts to work again.

6. Due to the different temperatures of the two temperature sensors, the second temperature sensor 16 fluctuates between-0.1 and-0.3 ℃, and the first temperature sensor 15 fluctuates between 0.1 and 0.3 ℃, and after the fluctuation state can be maintained for 30min, the freeze-thaw interface is shown to be present at the shearing surface.

7. At this time, the shear control device of the direct shear apparatus was started to start the shear test. Because a tiny gap exists between the upper shearing box and the lower shearing box in the shearing process (in the shearing process, in order to prevent the upper shearing box and the lower shearing box from being frozen together, a thin layer of vaseline is coated at the contact part of the upper box and the lower box, so that the tiny gap is formed), the freeze-thaw interface can be considered to be completely overlapped with the shearing surface, and the requirement of test precision is met.

FIG. 5 is a finite element simulation result of shear plane temperature. The shearing box is made of organic glass materials, the soil body is made of silty clay, the lower boundary temperature is set to be-4, -5, -6 and-8 ℃ respectively, the initial temperature of the soil body is set to be 5 ℃, and the heat conduction model is a Fourier unsteady state heat conduction model. As can be seen from FIG. 5, when the temperature of the middle position of the shearing surface reaches 0 ℃, the temperature fluctuation of the whole shearing surface is within 0.1 ℃ except that the temperature fluctuation of the position close to the edge is large, and the precision requirement of the soil body freeze-thaw interface shearing test can be completely met.

The technical solutions provided by the present application are described in detail above. The principles and embodiments of the present application are explained herein using specific examples, which are provided only to help understand the structure and the core concept of the present application. It should be noted that, for those skilled in the art, it is possible to make several improvements and modifications to the present application without departing from the principle of the present application, and such improvements and modifications also fall within the scope of the claims of the present application.

Claims

1. The utility model provides a soil body freeze thawing interface direct shear test device, includes shear box (2), shear box (3) down, refrigeration mechanism, temperature measurement part and temperature controller (17), its characterized in that: the refrigeration mechanism is arranged at the bottom of the lower shearing box (3), the temperature measuring components are respectively arranged on the side walls of the upper shearing box (2) and the lower shearing box (3) close to the shearing surface, and a micro gap is formed between the upper shearing box and the lower shearing box after the assembly is finished; and the temperature controller (17) is connected with the refrigerating mechanism and the two temperature measuring components and is used for controlling the working condition of the refrigerating mechanism according to the real-time temperature values of the two temperature measuring components after the preparation work is finished so as to enable the two temperature measuring components to reach respective preset target temperature values, and further forming a freeze-thaw interface.

2. The apparatus according to claim 1, wherein the cooling mechanism comprises a semiconductor cooler (11) and a cold storage plate (10) provided on the semiconductor cooler (11), and an upper surface of the cold storage plate (10) is in direct contact with the soil sample in the lower shear box (3) in operation.

3. The apparatus according to claim 2, wherein the refrigeration mechanism further comprises a heat sink (12) provided at the bottom of the semiconductor refrigerator (11).

4. The apparatus according to claim 2, wherein the refrigerating mechanism further comprises a heat conductive silicone rubber provided between the semiconductor refrigerator (11) and the cold storage plate (10).

5. The device according to claim 1, characterized in that said upper shear box (2) and said lower shear box (3) are made of a material with a low thermal conductivity.

6. The apparatus of claim 5, wherein the low thermal conductivity material is plexiglass.